Exfoliation and cleansing of the skin is an essential element of body care. Exfoliating compositions are well known in the art. Such compositions may, by abrasion, remove residual make-up and dead cells from the surface of the skin in order to prevent pores clogging. This is achieved by abrasive particles suspended in said compositions.
In the past, two particulate abrasive materials were used; calcium carbonate and the endocarp of apricot seeds. It was recently recognized that these abrasive materials had an inherent grittiness and that it was desirable to produce an abrasive material which has an initial skin feel which would disappear while using the cosmetic formulation.
Thus, it has been disclosed in EP-A-670,712 an exfoliating composition including a particulate exfoliating material with a particle size in the range of 0.03 to 3mm, wherein the particulate material comprises an agglomerated silica having a primary particle size in the range of 0.01-0.2 microns, which is friable and under conditions of use of the composition break up into particles having an average size of less than 40 microns.
Only one type of silica agglomerate is disclosed in this document and it is described as an agglomerate of Sident 22S.
It is disclosed in this document that the inherent grittiness of the suspended abrasive particles is avoided. It is further disclosed that particles with average size of less than 40 microns do not feel gritty and that the average particle size, after break up of the exfoliating particles, will be less than 40 .mu.m.
Nevertheless, it has been found that, whilst the grittiness is reduced, the particles are still felt by the user as a residue on the skin.
A desirable feature following particle breakdown would be the perception by the user of a creamy smooth lather of the product on the skin and gentle cleansing. It has been found that the use of silica agglomerates as described in EP-A-670,712 did not give this effect because they do not fully breakdown and therefore do not contribute, by way of a thickening effect that smaller particles can provide, to the resultant lather.
There is therefore a need for exfoliating particles which, whilst providing the required exfoliating performance, progressively break down to a point at which they are no longer detected. It is also desirable for such exfoliating particles to give a creamy, smooth lather on breakdown in a cosmetic composition.
Tests and Definitions
i) Oil Absorption
The oil absorption is determined by the ASTM spatula rub-out method (American Society Of Test Material Standards D, 281). PA1 The weight mean particle size of the water insoluble particulate before agglomeration is determined using a Malvern Mastersizer model X, made by Malvern Instruments, Malvern, Worcestershire with MS15 sample presentation unit. This instrument uses the principle of Fraunhoffer diffraction, utilising a low power He/Ne laser. The water insoluble particulates are dispersed ultrasonically in water for 7 minutes to form an aqueous suspension and then mechanically stirred before they are subjected to the measurement procedure outlined in the instruction manual for the instrument, utilising a 45 mm lens in the detector system. PA1 The Malvern Particle Sizer measures the weight particle size of the water insoluble particulate. The weight mean particle size (d.sub.50) or 50 percentile, the 10 percentile (d.sub.10) and the 90 percentile (d.sub.90) are easily obtained from the data generated by the instrument. PA1 EP-A-670712 describes a test to measure agglomerate strength in dry powder conditions. It is considered that this test is not representative of the conditions which prevail when a cosmetic composition is used and the granules are breaking down in an aqueous system. PA1 It was therefore necessary to develop a more representative test, which is carried out in the presence of water and subjects the granule to controlled de-aggregration. PA1 Granule breakdown characterisation was carried out using a Microson XL2020 Sonicator programmable ultrasonic liquid processor, manufactured by Misonix Inc. Farmingdale, N.Y. and supplied in the UK by Labcaire Systems Ltd, Avon. PA1 The Microson XL2020 Sonicator ultrasonic processor has a maximum of 550 watts output with a 20 KHz convertor and is fitted with a 3/4 inch tapped horn. The processor has variable amplitude control and a microprocessor controlled digital timer integrated with a Pulsar cycle timer with power output and elapsed time displays. PA1 The piezoelectric convertor transforms electrical energy to mechanical energy at a frequency of 20 KHz. Oscillation of piezoelectric crystals is transmitted and focused by a titanium disrupter horn that radiates energy into the liquid being treated. A phenomenon known as cavitation, the formation and collapse of microscopic vapour bubbles generated by the strong sound waves produces a shearing and tearing action. Almost all of the activity takes place just in front of the probe tip. PA1 The generator provides high voltage pulses of energy at 20 KHz and adjusts for varying load conditions, such as viscosity and temperature. It senses impedence change and increases or decreases power to the probe tip automatically. PA1 The 3/4 inch probe is a medium intensity horn for processing volumes between 25 and 500 ml. The maximum amplitude at the tip of the probe is 60 microns. Hence, sonicator processors operating at output control setting 10 have 60 microns of amplitude (peak to peak amplitude of the radiating face of the tip) at the tip of the probe. PA1 Therefore, there is a linear relationship between the output control knob (or amplitude adjustment knob) and the amplitude at the tip of the probe., ie 6 micons of amplitude per control knob setting. The generator draws energy accordingly to maintain a constant amplitude at the tip for a given output control setting. This is displayed on the % output power meter and is energy in Watts (ie output=%/100*550 watts available=x watts delivered) PA1 A paper given by Mr S Berliner, (Director, Technical Services, Heat Systems-Ultrasonics Inc.) at the 9th Annual Technical Symposium of the Ultrasonic Industry Association, entitled "Application of Ultrasonic Processors (Power vs Intensity in Sonification)" provides further detailed information of the principles involved in this experimental technique. PA1 A 250 ml pyrex beaker is insulated and fitted with a lid with a 3/4 inch hole in the centre to accommodate the ultrasonic probe and a 1/8 inch hole to the side to accommodate a temperature probe. PA1 When the cavitation process is complete, the stirrer is switched off and the magnetic stirrer bar is removed. Manual stirring is continued with a spatula to maintain dispersion. PA1 An accurate measure of the true particle size distribution of the granular composition is done using sieve analysis. PA1 100 g of the sample is placed on the top sieve of a series of BS sieves, at approximately 50 micron intervals to cover the particle size range of the granule. The sieves are arranged in order with the finest at the bottom and the coarsest at the top of the stack. The sieves are placed in a mechanical vibrator eg Inclyno Mechanical Sieve Shaker by Pascall Engineering Co. Ltd., covered with a lid and shaken for 10 minutes. Each sieve fraction is accurately weighed and the results calculated: ##EQU2## PA1 Surface area is determined using standard nitrogen adsorption methods of Brunauer, Emmett and Teller (BET), using a single point method with a Sorpty 1750 apparatus supplied by Carlo Erba company of Italy. The sample was outgassed under vacuum at 270.degree. C. for 1 hour before measurement.
The test is based on the principle of mixing linseed oil with the silica by rubbing with a spatula on a smooth surface until a stiff putty-like paste is formed which will not break or separate when it is cut with a spatula. The volume of oil used is then put into the following equation: ##EQU1##
ii) Weight Mean Particle Size
iii) Granular Strength
Procedure:
Into the insulated beaker weigh the desired amount of deionised water, maintained at a constant temperature of 21.degree. C. and the desired amount of inorganic granule to obtain a final weight of 200 g. A magnetic stirrer bar is introduced into the beaker and the beaker is placed on a magnetic stirrer hotplate equipped with a temperature sensor (Heidolph MR3003 magnetic stirrer hotplate with a stainless steel PT-100 temperature sensor and rpm stirrer speed, obtainable from Orme Scientific, Manchester. The beaker contents are stirred on setting 3 (.about.300 rpm), the ultrasonic probe is immersed to a depth of 5/8 inch into the liquid and the temperature sensor is inserted into the liquid to continuously monitor temperature.
The Sonicator ultrasonic processor is switched on and information on processing time and pulsed mode programmed, as required.
Cavitation is introduced to the system by turning the output control knob to the desired amplitude setting, whilst the temperature profile is closely monitored. The % power output required to maintain the amplitude at the tip is also recorded, according to the setting.
+45 micron Wet Sieve Test Method
The inorganic particle dispersion is poured through a 45 micron sieve. Any residue in the beaker is washed through the sieve, using half the amount of initial water. The sieve is then dried to constant weight in an oven at 105.degree. C. The residue which remains on top of the 45 micron sieve is then weighed and expressed as a percentage of the initial weight of inorganic granule. The greater the amount retained on the sieve, the stronger the agglomerate strength of the granule and the more difficult it is to breakdown. An optimum product will have no residue remaining on the sieve.
It has been found that, for a granule to satisfactorily breakdown in cosmetic compositions, it will have less than 5%, preferably less than 2%, most preferably less than 1% by weight, residue on a +45 micron sieve after ultrasonification on setting 10 (60 micron amplitude) for a period of 7 minutes.
iv) Particle Size Distribution by Sieve Analysis
v) BET Surface Area